This research attempts to understand the unique retinoid biochemistry of human RPE maintained in tissue culture. It builds on our previous findings that human RPE rapidly loses it large retinoid stores in culture, that the loss can be prevented by removing lipid acceptor molecules from the media, that the stores can be reestablished by retinoid supplementation and that the cells can isomerize, esterify, hydrolyze, oxidize and release incorporated retinoids. The isomerization, 11-cis retinyl ester hydrolysis and 11-cis retinol oxidation involve stereospecific enzymes, the oxidation being facilitated by the 11-cis retinal binding protein (CRALBP). In this research we shall determine whether the formation of 11-cis isomers varies with time in culture, how it is influenced by preventing or provoking retinoid release, whether 11-cis retinol and retinal are also released, whether release is affected differently by different lipid acceptors, (albumin versus interstitial retinoid binding protein (IRBP), whether such acceptors can transfer retinoids to co- cultured outer segments, and if this occurs, whether there is stereospecificity. We shall determine whether photic bleaching of CRALBP influences the oxidation of 11-cis retinol in the intact cells, as implied by in vitro studies and whether 11-cis retinol in the cytosol of these cells is bound to a specific protein. We shall subcellular fractionate and attempt to purify those proteins unique to 11 cis retinoid metabolism. Our main goal is to establish quantitative relationships for retinoid metabolism in cultured RPE and to identify and isolate the specific proteins involved in this process in order to be in a better position to understand genetic and/or toxic disease of human RPE.